Method for producing regenerated cellulose products



United States Patent Office 3,351,696 Patented Nov. 7, 1967 3,351,696 METHOD FOR PRODUCING REGENERATED CELLULOSE PRODUCTS Nicolas Drisch, Paris, France, assignor to CTA-Compagnie lndustrielle de Textiles Artificels et Synthetiques, a corporation of France No Drawing. Filed July 18, 1963, Ser. No. 296,117 Claims priority, application France, July 20, 1962, 904,601 3 Claims. (Cl. 264-195) US. patent application Serial No. 104,789 filed April 24, 1963, and now abandoned, corresponding to French Patent No. 1,266,492 dated April 22, 1960, describes a process for the manufacture of regenerated cellulose filaments belonging to the group of polynosic fibres, having a very high tenacity, both in the conditioned state and in the wet state, a good dimenisonal stability, a high modulus of elasticity in the wet state and a low degree of swelling, the process consisting essentially in spinning a highly viscous viscose having a high gamma index and containing a cellulose of high degree of polymerisation, in a bath with a low acid content and in the presence of an aldehyde, the latter being incorporated into the spinning bath and/ or into the viscose.

According to the invention which forms the subject of the present application, there are obtained threads or yarns of even better characteristics, particularly threads or yarns having high strength both in the conditioned and in the wet state, by spinning viscoses such as those described in the above mentioned French patent in weakly acid cold baths and in the presence of an aldehyde, the essential feature of the invention being that this aldehyde is not present in the spinning bath, but on the contrary in an intermediate bath disposed between the spinning bath and the second bath serving especially for the setting after drawing. In addition, the present process is characterized by the use of means enabling the freshly spun filaments to be hydroextracted, on the one hand for preserving in them a highest possible gamma index and, on the other hand, for increasing their power of absorption with respect to the intermediate bath containing an aldehyde.

It has already been indicated in French Patents Nos. 993,756 and 1,068,692 that the very dilute acid baths essentially have a coagulating action on the freshly spun filaments and only a slight action in regeneration. Under these conditions, the filaments may be strongly drawn or stretched between the first spinning bath and the second regeneration bath. On the other hand, the addition of aldehydes to the spinning bath and/ or to the viscose retards the decomposition of the viscose by formation of a more stable complex of the xanthate.

Thus, in the case of formaldehyde, there is probably formed a cellulose methylenebis-xanthate or a methylol derivative Ce11OfiS-CH2OH s which are more stable in acid medium.

By the combination of the two elements: 1) a bath which is essentially or exclusively coagulating and (2) spinning in the presence of an aldehyde, which combination has formed the subject of the parent patent, the result is achieved of retarding and considerably slowing down the decomposition of the Xanthate in the spinning bath. Under these conditions, it has been possible for the filaments in the state of a gel to be drawn by 200% and more, this drawing being made possible by the fact that the yarn leaving the first bath still has a very high gamma index, and it is in a particular state of plasticity.

Nevertheless, the incorporation of the formaldehyde into the first spinning bath is prejudicial to a good spinning operation, because this compound reacts with the hydrogen sulphide and the decomposition products of the trithiocarboxylic acid in order to give the hydroxymethyl mercaptan; this latter, by condensation, is converted into trithiane, which is deposited on the spinnerets and the spinning members, and this quickly makes the spinning unworkable, unless the bath is continuously cleaned, which is a costly operation.

On the other hand, if a similar cold first bath but without formaldehyde, is used, and if the freshly spun filaments, still with a very high gamma index, are conducted into an intermediate bath containing an aldehyde, the stable complexes referred to are formed in the intermediate bath, this making it possible to effect the drawing under favorable conditions.

It follows from this that the pollution of the first bath is thus avoided, while permitting the formation of the xanthate complex. In actual fact, from the quantitative point of view, the conditions of formation of the xanthate complex are less favorable in the intermediate bath than in the first bath, because it is not possible to avoid a drop in the gamma index during the interval of passing between the two baths. The result is that the gamma index is stabilized at a lower level in the case of the intermediate bath, but this level is still relatively high, and it permits much greater drawing effects than when the spinning is effected in the absence of formaldehyde.

As has just been mentioned, it is impossible to avoid a drop in the gamma index in the interval of travelling between the first bath and the intermediate bath, because the bath entrained by the filaments in the gel state continues, although slowly, to decompose the cellulose xanthate. On the other hand, in order that. the filaments in the gel state may quickly absorb the maximum of aldehyde during the passage thereof in the intermediate bath, and as a result be converted more completely into stable xanthate complex, it is also necessary to free them as far as possible from the liquid which impregnates them and which originates from the first bath. According to another feature of the invention, this double result is obtained by simple means, such as hydroextraction (e.g., by wiping off the liquid bath adhering to the freshly spun gel filaments) or air suction.

For example, the freshly spun filaments can be subjected to a compressing action by means of rollers under a pressure sufficient to obtain the desired effect without any deformation of the filaments being produced. It is even possible to cause the filaments to travel over a finely perforated roller, the interior of which is under vacuum, the said roller comprising an internal screen on the parts not covered by the filaments.

It is necessary to point out that the effect obtained by the intermediate bath and by the hydroextraction can be further improved if the spinning conditions are suitably chosen. It is then possible to have just before entry into the second bath, gamma values which are at least equivalent if not higher than those which are obtained with the process according to the parent patent.

Thus, the use of a colder bath, containing less acid, and by addition of small quantities of zinc sulphate, coupled with the use of an intermediate bath, makes it possible for very high gamma values to be maintained before entering the second bath. The following Table indicates the comparative gamma values for a spinning according to the parent patent, a spinning according to the new process (corresponding to the following example) and a spinning in the complete absence of formaldehyde:

The figures on this table clearly indicate that it is even possible to attain a very high gamma value when the formaldehyde in introduced into an intermediate bath.

As in connection with the parent patent, the present invention is carried out with a viscose which contains at least 3% of cellulose and at least 1.5% of caustic soda and of which the rate of sulphidation is 35% at least, relatively to the alpha-cellulose being used. The gamma index of the viscose at the time of spinning must be between 45 and 100 and preferably between 55 and 90. The cellulose contained in the viscose must have a degree of polymerisation of at least 400 and preferably higher than 500 and be as free as possible from short chains. The viscosity of the viscose at the moment of spinning is at least equal to 150 poises and it is preferably higher than 400 poises. The viscose is spun in a first bath which contains less than 60 g./l. and preferably 8 to 40 g./l. of sulphuric acid, 10 to 120 g./l. of sodium sulphate and also small quantities (less than 1%) of zinc sulphate, but not containing any aldehyde. The temperature of the first bath is between 5 and 40 C., preferably between 8 and 30 C.

After having left the first bath, the filaments are hydroextracted in one or more stages by means of roller systems or by a suction means or by any other means, and they pass in one or more stages into a cold diluted acid intermediate bath containing from 1 to 40 g./l. of an aldehyde per litre. This intermediate bath may moreover have the same composition as the first bath from the point of view of the content of acids and sulphates. The filaments then enter a second hot dilute acid bath and optionally into a third degasification bath. A drawing of at least 100% and preferably of at least 200% is applied to the filaments by the usual means in the first bath and/ or in the second bath and/ or during the passage through air between the first and second baths.

The process which has just been described is adapted for the manufacture of rayon, but it is particularly suitable for the spinning of staple fibres. In this case, after the cutting in the acid state, the fibres are subjected to a relaxation treatment with caustic soda, in the primary swelled state, under the conditions indicated in the first addition; they are then desulphided, degreased and dried.

The fibres manufactured according to the process described have a high strength which reaches at least 4 g./den., when conditioned, and 3.5 g./den., when wet. They have a high modulus of elasticity, which is shown by an elongation in the wet state below 4% under a load of 0.5 g./den., and they are circular in section. By an appropriate treatment in 70% nitric acid, it is found that the fibres obtained have a very characteristic fibrillar structure, much closer to that of cotton than to that of other regenerated cellulose fibres. Examination with X-rays, and also the measurements of birefringence, and of accessibility (formylation), etc. show the existence of an orientated structure which does not however affect the resistance to repeated fiexions. These structural characteristics are not modified in practice by a subsequent treatment with 5% caustic soda, whereas under the same conditions the ordinary rayon and staple fibres are greatly disarranged. The fabrics obtained from the fibres which have been described have an excellent stability with respect to repeated washing.

One embodiment of the process according to the invention will now be described, it being understood that this example is not limitativc in any way and that the invention covers any other modification within the same scope. Thus, the invention is also applicable to the manufacture of regenerated cellulose articles other than textile rayon, rayon for pneumatic tyres, films, etc.

Example A wood pulp having a content of 97.5% of alphacellulose is steeped for 30 minutes in 242 g./l. of soda at 20 and is pressed at a ratio of 3.1 with respect to the alpha-cellulose. The alkali-cellulose obtained is comminuted and is immediately treated with thiocarbonate, without any previous ripening, using 45% of carbon di sulphide (with respect to the cellulose). The xanthate formed is then dissolved in dilute caustic soda while continuing the thiocarbonation with the supplementary introduction of 10% of carbon disulphide. In this way, there is obtained a viscose with 5.75% of cellulose and 4.2% of caustic soda, having a viscosity of 600 poises, a gamma index of and containing a cellulose of DP 550.

The viscose is then spun through a tube, using a spinneret having 8000 holes, into a spinning bath at 15 C. and containing 22 g./l. of sulphuric acid, g./l. of sodium sulphate, 1 g./l. of zinc sulphate and also small quantities of Ceponol (sodium alkyl-aryl-sulfonate). The filaments formed are extracted from the first bath, then hydroextracted by means of a comprising roller system, and they are conducted into an intermediate bath at 20, which contains the same quantities of acid, sodium sulphate and zinc sulphate as the first bath, and also 10 g. of formaldehyde per litre. The bundle of filaments then passes into a second dilute acid bath which is very hot C.) and contains a little formaldehyde entrained from the intermediate bath, and then into a degasifying bath. The total drawing between the first bath and the second bath is 208%, allowing for a slight detensioning in the degasifying bath. Finally, the roving then enters a container at a speed of 15 m./ min.

The roving is then cut into discontinuous fibres, which are subjected to a relaxation treatment with 53 g./l. of caustic soda at 30 C. The fibres are then washed, desulphided, degreased and dried; they have the following characteristics:

Count, den. 1.51

Fibres of 1.5 den/40 mm., obtained by the process which has just been described, were converted into yarns of the metric number 50, twist 790 t./m., and the latter were woven with a cotton warp to give a fabric of weave 35/30, weighing 118 g. per square metre.

On the other hand, fibres of the same count and of the same staple length, obtained by a similar process but without the intermediate bath and in the complete absence of formaldehyde were converted in the same way into yarns of number 50, and these latter were woven with a cotton warp, as indicated before. The following table indicates the comparative features of the yarns and of the fabrics obtained with these two types of fibres:

1 Intermediate bath with formaldehyde. 2 In complete absence of formaldehyde.

As Will be seen from this table, the fibres according to the invention are clearly superior to the fibres spun Without intermediate bath. The fabrics obtained with these fibres, in addition to the advantages referred to, have an excellent dimensional stability, which is not affected by washing With strongly alkaline solutions.

What is claimed is:

1. A process for the production of filaments of regenerated cellulose having a very high tenacity both in the conditioned state and in the wet state, good dimensional stability, a high modulus of elasticity in the Wet state, which comprises spinnning a viscose which contains a cellulose whose DP is equal to at least 500, and having a viscosity of 150 poises to 1000 poises and a gamma number of 45 to 100 into a first bath containing less than 60 grams per liter of sulphuric acid, to 120 grams per liter of sodium sulphate and less than 1% zinc sulphate to produce filaments, introducing the filaments so formed into an intermediate bath containing from 1 to grams per liter of an aldehyde, introducing the filaments from said intermediate bath into a second hot regenerative bath and stretching said filaments 100% of their length at a stage prior to removal from said second bath, and fixing said stretched filaments.

2. The process set forth in claim 1 in which the aldehyde is formaldehyde.

3. A process for the production of filaments of regenerated cellulose having a very high tenacity both in the conditioned state and in the wet state, good dimensional stability and a high modulus of elasticity in the wet state, which comprises spinning a viscose which contains a cellulose Whose DP is equal to at least .500, and having a viscosity of at least 400 poises and a gamma number of to into a first bath containing from 8 to 40 grams per liter of sulphuric acid, 10 to grams per liter of sodium sulphate and less than 1% zinc sulphate to produce filaments, introducing the filaments so formed into an intermediate bath containing from 1 to 40 grams per liter formaldehyde, introducing the filaments from said intermediate bath into a second hot regenerative bath and stretching said filaments by at least 200% of their length at a stage prior to removal from said second bath, and fixing said stretched filaments.

References Cited UNITED STATES PATENTS 2,452,130 10/1948 Kayser 264-198 2,974,363 3/1961 Meyer 264l97 2,979,767 4/1961 Fry 264-198 3,007,766 11/1961 Elssn-er et a1 264197 3,038,778 6/ 1962 Daimler et :al 264-197 3,139,467 6/1964 Drisch et al. 264

ALEXANDER H. BRODMERKEL, Primary Examiner. J. H. WOO, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF FILAMENTS OF REGENERATED CELLULOSE HAVING A VERY HIGH TENACITY BOTH IN THE CONDITIONED STATE AND IN THE WET STATE, GOOD DIMENSIONAL STABILITY, A HIGH MODULUS OF ELASTICITY IN THE WET STATE, WHICH COMPRISES SPINNING A VISCOSE WHICH CONTAINS A CELLULOSE WHOSE DP IS EQUAL TO AL LEAST 500, AND HAVING A VISCOSITY OF 150 POISES TO 1000 POISES AND A GAMMA NUMBER OF >45 TO 100 INTO A FIRST BATH CONTAINING LESS THAN 60 GRAMS PER LITER OF SULPHURIC ACID, 10 TO 120 GRAMS PER LITER OF SODIUM SULPHATE AND LESS THAN 1% ZINC SULPHATE TO PRODUCE FILAMENTS, INTRODUCING THE FILAMENTS SO FORMED INTO AN INTERMEDIATE BATH CONTAINING FROM 1 TO 40 GRAMS PER LITER OF AN ALDEHYDE, INTRODUCING THE FILAMENTS FROM SAID INTERMEDIATE BATH INTO A SECOND HOT REGENERATIVE BATH AND STRETCHING SAID FILAMENTS 100% OF THEIR LENGTH AT A STAGE PRIOR TO REMOVAL FROM SAID SECOND BATH, AND FIXING SAID STRETCHED FILAMENTS. 